JPH0746752B2 - Anisotropic conductive adhesive - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric circuit, particularly a liquid crystal display (LCD) and a flexible printed circuit board (FPC), or a hard wiring board (PCB) and F.
The present invention relates to an anisotropic conductive adhesive used for connecting a PC or the like.

[0002]

2. Description of the Related Art In recent years, electronic and electric devices have become smaller and thinner, and have come to be used in various environments such as inside and outside of automobiles, and high reliability is required for connection between electronic and electric circuits. Became. To meet this requirement, conductive particles used for anisotropic conductive adhesives are metal powders such as nickel and plastic balls whose surface is made as uniform as possible and whose surface is coated with gold or the like having low contact resistance. It became so.

[0003]

However, noble metal plating such as gold is very expensive, and when metal powder is used, the density difference with the adhesive component is large and separation is likely to occur during production. It had the drawback of being poor in sex. The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide an anisotropic conductive adhesive which is inexpensive, has high reliability of connection, and has good workability during manufacturing.

[0004]

Means for Solving the Problems The present inventors have found that the reliability of the connection in the anisotropically conductive adhesive, in its shape than the material of the conductive particles, the internal stress temperature, due to environmental changes such as humidity and The inventors have found that it suffices to eliminate the microscopic movement of the conductive particles due to external force such as vibration and drop, and have completed the present invention, which is an anisotropic conductive material composed of an insulating adhesive and conductive particles. in the adhesive, conductive particles are carbon
Composites made by firing and graphitizing organic matter after attaching organic substances to the particles.
The gist is an anisotropic conductive adhesive characterized by being particles having a number of protrusions .

The electrically conductive particles used in the present invention are required to be reliable in connection for a long period of time, and therefore it is preferable to use chemically stable carbon particles. Further, in order to suppress microscopic movement due to environmental changes and external forces, it is necessary to provide a plurality of contact points, preferably three or more contact points, with the electrode to be connected. Therefore, the shape of the carbon particles has many protrusions. I shall. If the projections are too small or too small, the effect of controlling microscopic movements against various forces becomes small. Therefore, the projections protruding by 0.5 μm or more, preferably 2 μm or more from the inscribed sphere of the conductive particles are used. It is preferable to have four or more per piece. The inscribed sphere here means the largest sphere that can be contained inside the particle. The particle size of the conductive particles should be as uniform as possible. However, if the particle size is too large or the compounding amount is too large, a short circuit is likely to occur between adjacent electrodes, so the particle size should be selected from the range of 5 to 100 μm. However, the particle size of the particles having protrusions is the outer diameter including the protrusions, that is, the diameter of the circumscribing sphere, in other words, the diameter of the smallest sphere that can contain the particles inside. The compounding amount is preferably 50 to 500 per 1 mm ² when the anisotropic conductive adhesive is placed on the connection electrode. It is desirable that the conductive particles have high strength because the load concentrates on the protrusions during pressure contact.
The strength at 10% compression is 10 kgf / mm ² or more, preferably 15 kgf / mm ² or more.

As a method for producing such carbon particles, spherical carbon particles serving as nuclei, for example, spherical mesocarbon micro-beads produced as a by-product in the process of refining pitch, spherical particles obtained by methods such as bulk polymerization and suspension polymerization An example is a method in which an organic substance is adhered to a carbonized product obtained by baking a resin and then baking the resin at about 800 to 2500 ° C. At this time, it is preferable to use tar, pitch, or the like as the organic substance attached to the carbon particles serving as nuclei, because graphitization is easy.

The conductive particles are in a state of being dispersed in the adhesive component until the electrodes are connected by the adhesive, but when the connection is made, the surrounding adhesive component is excluded and the electrodes are connected to each other. The adhesiveness or adhesiveness with the adhesive component is preferably poor, and it is preferably surface-treated with a silicone resin, a fluororesin or the like. However, if the release agent coating is too thick, the conductivity is impaired, so the coating thickness is preferably 1 μm or less, preferably 0.1 μm or less, and it is sufficiently effective not to cover the entire surface of the conductive particles.

The electrically insulating adhesive used to disperse the conductive particles includes ethylene vinyl acetate copolymer resin, carboxyl modified ethylene vinyl acetate resin, ethylene-acrylate copolymer resin, ethylene-ethyl acrylate copolymer, ethylene-isobutyl. Acrylate copolymer, polyamide resin, polyester resin, polymethyl-methacrylate resin, polyvinyl ether resin, polyvinyl butyral resin, polyurethane resin, styrene butadiene styrene block copolymer (SBS), carboxyl modified SBS, styrene isoprene styrene copolymer resin (SI
S), styrene-ethylene-butylene styrene copolymer resin (SEBS), maleic acid modified SEBS, polybutadiene rubber, chloroprene rubber (CR), carboxyl modified CR, styrene-butadiene rubber, isobutylene-isobrene copolymer, carboxyl modified nitrile rubber It is prepared by using one kind or a combination of two or more kinds selected from epoxy resin, silicone rubber and the like as a main ingredient.

As the tackifier, rosin,
A rosin derivative, a terpene resin, a terpene phenol copolymer, a petroleum resin, a coumarone-indene resin, a styrene resin, an isobrene resin, an alkylphenol resin, a phenol resin, etc. are added as necessary as one kind or a combination of two or more kinds. . In addition, reactive auxiliaries, phenolic resins as crosslinking agents, polyols, isocyanates, melamine resins, urea resins, urotropins, amines, acid anhydrides, peroxides, metal oxides, chromium trifluoroacetate salts, etc. Organic acid metal salts, metal alkoxides such as Ti, Zr and Al alkoxides, organic metal compounds such as dibutyltin oxide, photoinitiators such as 2,2-diethoxyacetophenone and benzyl, amines, phosphorus compounds, chlorine compounds, etc. The sensitizer and the like are also appropriately selected and used as necessary.

The anisotropically conductive adhesive of the present invention is generally interposed between two opposing groups of electrodes on an electronic / electrical circuit board and pressed from above one of the electronic / electrical circuit boards, and simultaneously heated or exposed to light. , Irradiating an electron beam to activate the adhesive, fixing the two circuit boards with the adhesive, and electrically connecting the opposite electrode groups through conductive particles. Specifically, it is a glass such as a display panel, a metal such as an LSI chip, a metal oxide or polyimide, and a flexible printed circuit board based on a polyester resin. These surfaces have -O
H, -COOH, -C = O, due to the provision of a polar group such as -COOCH _3, the present adhesive, it is required to have an adhesive Correspondingly, as the solubility parameter 8.5 Above, especially above 9 are desirable. In adjusting these solubility parameters, an acrylic resin, a nitrile rubber, a crobrene rubber, an adhesive containing a vinyl acetate resin as a main component, since the base polymer alone has a high solubility parameter, it may be used as it is, but polyisobutylene, polybutadiene, In an adhesive containing a resin having a low solubility parameter such as polystyrene as a main component, it becomes possible to make the polarities suitable by adding a tackifier such as the above-mentioned phenolic resin.

In the anisotropically conductive adhesive of the present invention, when the adhesive component is a solvent-free solid state or high-viscosity liquid,
Dissolve this in an appropriate solvent and apply it directly on the electrode to be connected by a known method such as printing, coating or spraying, or after forming it on the separator, cut it to the desired size and connect it to the connection electrode. It is used after being transferred to a part, or when the adhesive component is in a liquid state, it is applied on the connection electrode during connection work. Here, when the anisotropic conductive adhesive according to the present invention is applied, the adhesive component is appropriately, for example, 50 to 5
00 is the viscosity adjusted to about poise, there is a flowable state, the viscosity is too there are differences in the density of the adjusted adhesive component and conductive particles, conductive particles are easy to separate by settling or floating, Conduction due to problems such as poor dispersion
The density of the conductive particles is 1 of the density of the adhesive component whose viscosity is adjusted.
/ 3 to 3 times, preferably 1/2 to 2 times. By the above, microscopic movement of conductive particles due to environmental changes, vibration, dropping, etc. is suppressed, and it is possible to obtain an anisotropic conductive adhesive that has high connection reliability for a long period of time and that has good manufacturing workability and is inexpensive. it can.

[0012]

Example 1 A spherical phenol resin having an average particle size of 30 μm was fired to produce carbon particles having an average particle size of 24 μm, and tar was used for 100 parts by weight of the carbon particles.
Add 20 parts by weight and stir in an inert gas atmosphere for 20
Burned at 00 ° C, average particle size 30μm with many protrusions
Thus, conductive particles having a density of 1.5 g / cm ³ were obtained. Next, styrene-ethylene-butylene-styrene copolymer rubber 10
5 parts by weight of terpene-phenolic tackifier 5
0 part by weight was added and dissolved in toluene to obtain a 25% by weight solution. At this time, the density of the adhesive solution is 1.1 g / cm ^3.
Met. To 100 parts by weight of this adhesive solution, an adhesive prepared by adding 1.5 parts by weight of the above-mentioned conductive particles was prepared.
Screen printing on an electrode group of the FPC in which a pattern of 0.3 mm pitch was formed on the ET film with silver paste and drying to form an anisotropic conductive adhesive layer having a thickness of 25 μm,
An FPC with an anisotropic conductive adhesive was obtained.

(Example 2) To 100 parts by weight of the conductive particles obtained in Example 1, 0.5 parts by weight of a fluororesin release coating agent diluted with 50 g of ethanol was added, and the mixture was heated to 70 ° C. After removing ethanol for 1 hour, 150 ℃
After heating for 1 hour, the surface of the conductive particles was subjected to a release treatment to obtain conductive particles.
Using the conductive particles, the same FPC with an anisotropic conductive adhesive as in Example 1 was obtained. The strength S10 (kgf / mm ² ) of each particle thus obtained at 10% compression is determined by the load P (kg
f) and the particle radius r (mm), S10 = (2.8 ×
P) / (πr ² ) found 18k on average
It was gf / mm ² (micro compression tester for powder PCT-
200, used by Shimadzu Corporation).

(Comparative Example 1) An FPC with an anisotropic conductive adhesive was obtained in the same manner as in Example 1 except that spherical carbon particles having an average particle diameter of 30 μm and having no protrusions were used as the conductive particles.

Hard wiring board (PC
B) and an ITD solid glass substrate having a surface resistance of 30 Ω were heat-sealed with the anisotropically conductive adhesive-attached FPC obtained in Examples 1 and 2 and Comparative Example 1 to perform initial and thermal shock tests (-30 ° C). Alternate between 30 minutes and 85 ° C for 30 minutes 200
The resistance value between the adjacent electrodes on the PCB side after the measurement (repeated twice) was measured, and the results are shown in Table 1.

[0016]

[Table 1]

[0017]

As is apparent from the above, by using the Kahhong particles having a large number of protrusions as the conductive particles, the conductivity caused by the difference in the thermal expansion of the adhesive, the circuit board to be connected, etc. due to the change of environment. The force to move the particles,
An anisotropic conductive adhesive that withstands external force such as vibration and drop and has high connection reliability can be obtained. Further, since the difference in density between the adhesive component and the conductive particles is small, separation does not occur during production and workability is good, which is effective in reducing production costs. Further, if the conductive particles are subjected to a mold release treatment, higher connection reliability can be obtained, and the anisotropic conductive adhesive of the present invention can be used in a wider range of electronic and electric devices.

Claims (3)

[Claims] 1. An anisotropic conductive adhesive comprising an insulating adhesive and conductive particles, wherein the conductive particles are carbon particles.
An anisotropic conductive adhesive, characterized in that it is a particle having a plurality of projections, which is obtained by adhering an organic substance to, followed by firing and graphitizing . 2. The projections of the conductive particles are of the conductive particles.
The projection including 0.5 mm or more protruding from the inner sphere and including the projection
The adhesive according to claim 1, wherein the conductive particles have a particle diameter of 5 to 100 µm . 3. The adhesive according to claim 1, wherein the conductive particles are subjected to a mold release treatment.